Patent document, JP 3541675, discloses an apparatus for detecting a disconnection of a winding of a motor, which is feedback-controlled based on an actual value of a current flowing in a winding of the motor and a current command value required for the motor to generate a predetermined torque.
This apparatus includes an integration part, which integrates a difference between the current command value and the actual current value, and an abnormality detection part, which detects an abnormality when an output value of the integration part exceeds a predetermined value. When a disconnection arises in a motor of a three-phase AC type for example, the difference between the current command value and the actual current value consistently arises and the output value of the integration part continues to increase. It is possible for this reason to determine the disconnection of the winding based on the output value of the integration part exceeding the predetermined value.
According to the apparatus described above, however, there are some cases, in which the disconnection cannot be detected when the motor is in a locked state. In the locked state, the motor cannot rotate in spite of a torque command and hence a rotation speed of the motor is very low. For example, in a hybrid vehicle or an electric vehicle, the motor is in the locked state, in which the vehicle is not braked and is maintained not to descend backward by operating an accelerator.
Even when no disconnection is present, the difference between the current command value and the actual current value is very little near zero ampere (0 [A]). In the locked state described above, the rotation speed of the motor is very low and the actual current value remains near 0 [A] for a long period of time.
For this reason, the disconnection cannot be detected when the actual current value is near 0 [A] in the locked state. Particularly the disconnection cannot be speedily detected even when the disconnection arises.